Field
Embodiments of the present disclosure generally relate to methods and apparatus for polishing a substrate, such as a semiconductor substrate. More particularly, to methods and apparatus for polishing an edge of a substrate in an electronic device fabrication process.
Description of the Related Art
Chemical mechanical polishing is one process commonly used in the manufacture of high-density integrated circuits to planarize or polish a layer of material deposited on a substrate by moving a feature side, i.e., a deposit receiving surface, of the substrate in contact with a polishing pad while in the presence of a polishing fluid. In a typical polishing process, the substrate is retained in a carrier head that urges or presses the backside of the substrate toward a polishing pad. Material is removed from the feature side of the substrate that is in contact with the polishing pad through a combination of chemical and mechanical activity.
The carrier head may contain multiple individually controlled pressure regions that apply differential pressure to different regions of the substrate. For example, if greater material removal is desired at peripheral edges of the substrate as compared to the material removal desired at the center of the substrate, the carrier head may be used to apply more pressure to the peripheral edges of the substrate. However, the stiffness of the substrate tends to redistribute the pressure applied to the substrate by the carrier head such that the pressure applied to the substrate may be spread or smoothed. The smoothing effect makes local pressure application, for local material removal, difficult if not impossible. Further, substrates may become non-planar during processing and, when polished in conventional systems, certain regions on the substrate may experience an over-removal or under-removal of material, which may be due to substrate quality, precision of polishing control, or other factors, each of which may damage portions of devices on the substrate thereby reducing yield.
Therefore, there is a need for a method and apparatus that facilitates removal of materials from local areas of a substrate.